Process of recovering the constituents of a polyvinyl chloride coagulating bath



United States Patent 3 Claims. (cl. 264-479 This invention relates to the wet-spinning of vinyl chloride polymers from their solutions in solvents of high boiling point which are sparingly soluble or insoluble in water.

It has been proposed to wet-spin solutions of polyvinyl chloride in cyclohexanone, especially using as the coagulation bath a mixture of equal parts of methanol and water. However, this process has not been industrially used, mainly because of the difiiculty of separating the constituents of the spinning bath by distillation. Since cyclohexanone forms an azeotrope with water, it is necessary to dry it before it can be used again as a solvent for more polyvinyl chloride.

The process of the present invention makes it possible to recover in a very simple manner the constituents of the coagulation baths. The new process comprises extruding a solution of a vinyl chloride polymer in cyclopentanone or cyclohexanone into an azeotropic mixture of water and a monohydric aliphatic alcohol containing three or four carbon atoms, preferably isopropyl alcohol, n-propyl alcohol or sec-butyl alcohol.

When the coagulation bath is distilled, the aliphatic alcohol distils first as an azeotrope with water, and may be immediately returned as such into the spinning bath, since it has the appropriate composition.

The solvent for the vinyl chloride polymer, e.g. cyclopentanone or cyclohexanone, is recovered in the anhydrous state from the bottom of the distillation column and can be reused immediately for dissolving more polyvinyl chloride. This ready separation of the constituents of the spinning bath and the possibility of immediately reusing them make it possible to use only small quantities of solvent and aliphatic alcohol.

The term vinyl chloride polymer is used herein to denote, besides polyvinyl chloride itself, polyvinyl chloride copolymers containing a major proportion of polyvinyl chloride, and derivatives of polyvinyl chloride obtained by superchlorination.

The spinning solutions may optionally contain substances intended to modify certain of the mechanical, physical, and chemical or dyeing properties of the filaments produced. The yarns and fibres obtained by the process of the invention may be finished in any appropriate operation and may be used alone, or blended with other natural or artificial (including wholly synthetic) fibres, in weaving or knitting or for the production of unwoven articles.

The following examples illustrate the invention.

EXAMPLE 1 A crystalline polyvinyl chloride polymer, obtained by polymerization at 15 C. and having an Afnor index of 3,337,670 Patented Aug. 22, 1967 130 (index determined at 25 C. in cy-clohexanone in accordance with the French standard NF T 51013), is dissolved in cyclohexanone to form a 25% solution. This solution is then heated to 140 C. and extruded through a spinneret having 260 holes each of a diameter of 0.06 mm. into a first bath having the composition of an isopropyl alcohol/water azeotrope (12.7% of water). The length of the bath is cm., the temperature 50 C., and the speed of the filaments leaving the bath is 13 m./ minute. The filaments then enter a second bath 15 cm. long of the same composition and temperature as the first. They leave this bath also at 13 m./ minute.

The filaments next enter a third bath identical to the second one, and a fourth bath, which is also the same except that its length is 20 cm.

Finally, the filaments enter a fifth bath 20 cm. long consisting of water at C. the filaments are wound up at 30 m./min. and then stretched three times their length in hot air at C. The filaments finally obtained have a breaking strength of 2.8 g./ den. and an elongation at break of 17%.

The various components of the coagulation baths are recovered by fractional distillation. The azeotrope of the isopropyl alcohol and water, which boils at 80 C., separates immediately from the cyclohexanone, which boils at 15 6 C. Thus, the isopropyl alcohol is recovered as its azeotrope with Water and the substantially anhydrous cyclohexanone is recovered in directly reusable form.

EXAMPLE 2 A 25% polyvinyl chloride solution in cyclopentanone is wet-spun into a coagulation bath having the composition of the n-propyl alcohol/water azeotrope (27% of water). The components of the coagulation baths are thereafter recovered as in Example 1, by fractional distillation. The azeotrope of the n-propyl alcohol, which boils at 87 C., separates immediately from the cyclopentanone, which boils at C.

EXAMPLE 3 A 12% solution in cyclohexanone of a vinyl chloride polymer having an Afnor index of 500 is wet-spun, using as coagulation bath the azeotrope of sec-butyl alcohol (30% of water). The various components of the coagulation baths are thereafter recovered, as in the preceding examples, by fractional distillation. The azeotrope of the sec-butyl alcohol, which boils at 88.5 C., separates immediately from the cyclohexanone which boils at 156 C.

We claim:

1. In a process for the production of filaments of a vinyl chloride polymer by extruding a solution of the polymer in a high boiling organic solvent into an aqueous coagulating bath, the improvement which comprises employing as the coagulating bath an azeotropic mixture of water and an aliphatic alcohol, which azeotropic mixture has a boiling point below that of the said solvent and of any azeotropic mixture formed by the said solvent with a component of the coagulating bath, fractionally distilling the coagulating bath after use to separate the water-alcohol azeotrope from high boiling solvent contained in it, and re-using the recovered azeotrope as a coagulating bath and the recovered high boiling solvent as spinning solvent in the production of vinyl chloride polymer filaments.

2. A process according to claim 1, wherein a solution of the polymer in a solvent selected from cyclopentanone or cyclohexanone is extruded into an azeotropic mixture of water and an aliphatic alcohol containing 34 carbon atoms in the molecule.

3. A process according to claim 2, wherein the solution is extruded into an azcotropic mixture of water and an aliphatic alcohol selected from n-propyl, isopropyl and sec-butyl alcohols.

4 References Cited UNITED STATES PATENTS 2,327,872 8/1943 Dahle. 2,953,818 9/1960 Bartron 264-178 3,078,242 2/1963 Morgan.

ALEXANDER H. BRODMERKEL, Primary Examiner.

DONALD J. ARNOLD, Examiner. 

1. IN A PROCESS FOR THE PRODUCTION OF FILAMENTS OF A VINYL CHLORIDE POLYMER BY EXTRUDING A SOLUTION OF THE POLYMER IN A HIGH BOILING ORGANIC SOLVENT INTO AN AQUEOUS COAGULATING BATH, THE IMPROVEMENT WHICH COMPRISES EMPLOYING AS THE COAGULATING BATH AN AZEOTROPIC MIXTURE OF WATER AND AN ALIPHATIC ALCOHOL, WHICH AZEOTROPIC MIXTURE HAS A BOILING POINT BELOW THAT OF THE SAID SOLVENT AND OF ANY AZEOTROPIC MIXTURE FORMED BY THE SAID SOLVENT WITH A COMPONENT OF THE COAGULATING BATH, FRACTINALLY DISTILLING THE COAGULATING BATH AFTER USE TO SEPARATE THE WATER-ALCOHOL AZEOTROPE FROM HIGH BOILING SOLVENT CONTAINED IN IT, AND RE-USING THE RECOVERED AZEOTROPE AS A COAGULATING BATH AND THE RECOVERED HIGH BOILING SOLVENT AS SPINNING SOLVENT IN THE PRODUCTION OF VINYL CHLORIDE POLYMER FILAMENTS.
 2. A PROCESS ACCORDING TO CLAIM 1, WHEREIN A SOLUTION OF THE POLYMER IN A SOLVENT SELECTED FROM CYCLOPENTANONE OR CYCLOHEXANONE IS EXTRUDED INTO AN AZEOTROPIC MIXTURE OF WATER AND AN ALIPHATIC ALCOHOL CONTAINING 3-4 CABON ATOMS IN THE MOLECULE. 